Q&A: I am not sure if I had a miscarriage or an ectopic pregnancy.

I'm going through a situation and have been getting different opinions from my OB/GYN and my Reproductive Endocrinologist. I have been trying to conceive for a year and was put on clomid. With the first cycle at 100 mg, I got a positive home pregnancy test. The first week or so after I had a positive test, I was having my HCG tested every 48 hrs and the levels looked normal. At about 5 weeks, I had an internal ultrasound, and the RE thought that it looked normal. The next week, however, I had another ultrasound, and the RE could no longer see the pregnancy. I went to the hospital for another round of ultrasounds, and the radiologist said that she saw no sign of a pregnancy, in my uterus or elsewhere and that I looked healthy.
I continued to have my HCG levels tested, and they continued to rise slightly throughout the next week. My RE was convinced that I just had a missed miscarriage. Last Friday (about 7 weeks pregnant), I had another internal ultrasound, and the RE said he could see just a sac--my HCG was 2900 (up from 2500 on Wednesday). This concerned my OB/GYN that I was having an ectopic, even though my RE is convinced that I am not, based on the sac in my uterus (he believes that the HCG was rising because of the presence of the sac). The RE also said that at 8 weeks pregnant, I would feel severe pain already if it was ectopic.
Anyway, my OB/GYN was too nervous, so he had me go in the next day for a D&C. He looked at the results with a pathologist, and didn't see any embryo matter, so he sent me for the Methotextrate shots.

I'm very confused because I don't know if I just miscarried--which would obviously be the preferable scenario-- or if I was, or could still be, suffering from an ectopic pregnancy. I had my HCG tested again yesterday, but haven't gotten the results.
Any thoughts or impressions that you could add would be appreciated.